Cooling device

ABSTRACT

An object of the present invention is to provide a cooling device that is easy to attach and that ensures intimate contact at a contact surface between a heat absorbing surface of a Peltier element and an object to be cooled and a contact surface between a heat radiating surface of the Peltier element and a cooling part. A cooling device according to the present invention includes a Peltier element having a heat absorbing surface and a heat radiating surface that are opposite each other; a heat absorbing plate having a first Peltier element attaching surface and located with the first Peltier element attaching surface facing the heat absorbing surface of the Peltier element; a heat radiating plate having a second Peltier element attaching surface and located with the second Peltier element attaching surface facing the heat radiating surface of the Peltier element; heat conducting members having viscosity or elasticity and provided between the heat absorbing surface and the first Peltier element attaching surface and between the heat radiating surface and the second Peltier element attaching surface; and a spacer provided between the heat absorbing plate and the heat radiating plate in parallel with the Peltier element and defining an opposing distance between the first and second Peltier element attaching surfaces.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to cooling devices, and particularly to a cooling device using Peltier elements.

2. Description of the Background Art

Peltier elements are temperature control devices that utilize the Peltier effect that heat moves from one metal to the other metal when an electric current is passed through the junction of the two kinds of metals. Cooling devices using Peltier elements can be small-sized. Also, Peltier elements can be current-controlled, so that they are suitable for the cooling of parts whose operating performance varies with temperature, such as semiconductor laser devices.

A Peltier element has two metal surfaces including a heat absorbing surface where heat absorption occurs and the temperature falls and a heat radiating surface where heat generation occurs and the temperature rises when a control current is passed. When using a Peltier element as a cooling device, an object to the cooled is located in contact with the heat absorbing surface of the Peltier element, and the heat radiating surface of the Peltier element is located in contact with a cooling part such as an air cooling or heat sink. When air exists at the contact surface between the heat absorbing surface of the Peltier element and the object to be cooled or at the contact surface between the heat radiating surface of the Peltier element and the cooling part, the efficiency of thermal conduction is reduced and the cooling performance is degraded. It is therefore necessary to bring the contact surfaces in intimate contact. While realizing intimate contact requires applying pressure, it is necessary to control the applied pressure such that it does not exceed the permissible pressure of the Peltier element, because the junction part of the Peltier element will be broken when subjected to excessive pressure.

Conventional structures for attaching Peltier elements include a simple attaching structure in which pressure is controlled by using screws to fix it. However, the Peltier element may be broken or the performance may be degraded when proper pressure cannot be applied to the Peltier element. As to a reason for such problems, the screwing torques may vary and the axial forces of screws may vary. Also, in a method in which commonly used screws are tightened diagonally to defined torque in some steps, the attached surfaces cannot be kept parallel and unbalanced load will be applied to the Peltier element. Also, attaching work takes time and productivity is lowered in the method of diagonally tightening screws to defined torque in some steps. In order to increase productivity, it is desired to provide a structure that is easy to attach and that ensures intimate contact at the contact surface between the heat absorbing surface of the Peltier element and the object to be cooled and the contact surface between the heat radiating surface of the Peltier element and the cooling part, by applying given pressure to the Peltier element in a range not exceeding the permissible pressure.

As to a conventional method of applying pressure to a Peltier element to realize intimate contact between the Peltier element and a heat generating object and the Peltier element and a heat conducting part, there is a cooling device having a pressurizing part that presses these constituent parts with pressure (for example, refer to Japanese Patent Application Laid-Open No. 2007-258520, page 1, FIG. 2, which is hereinafter referred to as Patent Document 1).

In Patent Document 1, the Peltier element, heat generating object, and heat conducting part are arranged in intimate contact as they are pressurized by the pressurizing part, but it does not disclose a method for ensuring intimate contact at the contact surface between the Peltier element and the heat generating object and the contact surface between the Peltier element and the heat conducting part.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a cooling device that is easy to attach and that ensures intimate contact at a contact surface between a heat absorbing surface of a Peltier element and an object to be cooled and a contact surface between a heat radiating surface of the Peltier element and a cooling part.

A cooling device according to the present invention includes a Peltier element having a heat absorbing surface and a heat radiating surface that are opposite each other, a heat absorbing plate having a first Peltier element attaching surface and located with the first Peltier element attaching surface facing the heat absorbing surface of the Peltier element, a heat radiating plate having a second Peltier element attaching surface and located with the second Peltier element attaching surface facing the heat radiating surface of the Peltier element, heat conducting members having viscosity or elasticity and provided between the heat absorbing surface and the first Peltier element attaching surface and between the heat radiating surface and the second Peltier element attaching surface, and a spacer provided between the heat absorbing plate and the heat radiating plate in parallel with the Peltier element and defining an opposing distance between the first and second Peltier element attaching surfaces.

According to the present invention, a cooling device includes a Peltier element having a heat absorbing surface and a heat radiating surface that are opposite each other, a heat absorbing plate having a first Peltier element attaching surface and located with the first Peltier element attaching surface facing the heat absorbing surface of the Peltier element, a heat radiating plate having a second Peltier element attaching surface and located with the second Peltier element attaching surface facing the heat radiating surface of the Peltier element, heat conducting members having viscosity or elasticity and provided between the heat absorbing surface and the first Peltier element attaching surface and between the heat radiating surface and the second Peltier element attaching surface, and a spacer provided between the heat absorbing plate and the heat radiating plate in parallel with the Peltier element and defining an opposing distance between the first and second Peltier element attaching surfaces, whereby the attachment is easy and intimate contact is ensured at the contact surface between the heat absorbing surface of the Peltier element and the object to the cooled and the contact surface between the heat radiating surface of the Peltier element and the cooling part.

These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a cooling structure for a laser light source device having a cooling device according to a first preferred embodiment of the present invention;

FIG. 2 is a cross-sectional view of the cooling device according to the first preferred embodiment of the present invention;

FIG. 3 is a cross-sectional view of the cooling device according to the first preferred embodiment of the present invention;

FIG. 4 is a cross-sectional view of a cooling device according to a second preferred embodiment of the present invention; and

FIG. 5 is a cross-sectional view of a cooling device according to a third preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described below referring to the drawings.

First Preferred Embodiment

FIG. 1 is a schematic diagram illustrating a cooling structure for a laser light source device having a cooling device 1 according to a first preferred embodiment of the present invention. As shown in FIG. 1, a laser light source device 11 is a semiconductor laser light source device that emits monochromatic laser light, and it generates heat while operating and the wavelength and power of the output light vary as the temperature varies. For example, the laser light source device 11 is used as a light source for a projection type display apparatus for displaying images in an enlarged manner. The laser light source device 11 is not limited to a semiconductor laser light source device, but it can be any light source device, such as an LED (Light Emitting Diode) device, for example. Also, while this preferred embodiment describes a cooling device for a light source device of a projection type display apparatus as an example, it is not limited to a projection type display apparatus but it is applicable to any device that can use the cooling device of this preferred embodiment.

A heat receiving plate 12 is located in contact with the laser light source device 11, and it receives the heat generated in the laser light source device 11. A heat absorbing plate 5 is a metallic plate, and it is located at a higher position than the heat receiving plate 12 (that is, the position where the heat absorbing plate 5 is set is higher than the position of the heat receiving plate 12). The heat receiving plate 12 and the heat absorbing plate 5 are connected through metallic heat pipes 13 that contain refrigerant inside. For example, the heat pipes 13 contain water as refrigerant at reduced pressure. With the heat received at the heat receiving plate 12 from the laser light source device 11, the water evaporates and moves upward (i.e. toward the heat absorbing plate 5) in the heat pipes 13. Then, the moved evaporated water condenses in the vicinity of the heat absorbing plate 5, and thus the heat transport from the heat receiving plate 12 to the heat absorbing plate 5 is enabled. The water condensed in the vicinity of the heat absorbing plate 5 returns to the heat receiving plate 12 because of the difference in height between the heat absorbing plate 5 and the heat receiving plate 12. In this way, the heat generated in the laser light source device 11 is received at the heat absorbing plate 5 through the heat receiving plate 12 and the heat pipes 13. In this preferred embodiment, water is contained in the heat pipes 13 as an example of refrigerant, but it is not limited to water but can be other refrigerant.

As shown in FIG. 1, a Peltier element 2 is provided between the heat absorbing plate 5 and a heat radiating plate 6 with heat conducting grease 4 (a heat conducting member) interposed therebetween. The heat radiating plate 6 is a metallic plate, and it receives the heat generated in the Peltier element heat radiating surface 2 b through the heat conducting grease 4. The Peltier element 2 performs heat absorption at the Peltier element heat absorbing surface 2 a, and performs heat radiation at the Peltier element heat radiating surface 2 b on the back of the Peltier element heat absorbing surface 2 a. The Peltier element heat absorbing surface 2 a is located facing the heat absorbing plate 5 through the heat conducting grease 4, and the Peltier element heat radiating surface 2 b is located facing the heat radiating plate 6 through the heat conducting grease 4.

The heat conducting grease 4 is highly heat conducting grease having viscosity, and it is a heat conducting member used to enhance the heat conducting efficiency by filling gaps formed because of the degree of flatness and the surface roughness at the contact surface between the Peltier element 2 and the heat absorbing plate 5 and the contact surface between the Peltier element 2 and the heat radiating plate 6. A Peltier element controller 10 is connected to the Peltier element 2 through a Peltier element control signal line 9, and the operation of the Peltier element 2 is controlled by a control signal sent from the Peltier element controller 10 to the Peltier element 2 through the Peltier element control line 9. The heat in the heat absorbing plate 5 is absorbed and cooled at the Peltier element heat absorbing surface 2 a, and the heat generated in the Peltier element heat radiating surface 2 b caused accordingly is conducted to the heat radiating plate 6. Spacers 3 are located between the heat absorbing plate 5 and the heat radiating plate 6 in parallel with the Peltier element 2. The cooling device 1 of this preferred embodiment includes the heat absorbing plate 5, the heat radiating plate 6, the Peltier element 2, the heat conducting grease 4, and the spacers 3.

A heat sink 15 is formed of a plurality of metal plates arranged in parallel, and it is a heat exchanger that dissipates heat by diffusing heat. A heat pipe 14 is connected between the heat sink 15 and the heat radiating plate 6, and the heat in the heat radiating plate 6 moves to the heat sink 15 through the heat pipe 14 and is dissipated in the heat sink 15 by thermal diffusion.

In this way, the heat generated in the laser light source device 11 is conducted to the heat absorbing plate 5 through the heat receiving plate 12 and the heat pipes 13. The heat absorbing plate 5 is controlled to certain temperature as it is cooled by heat absorption at the Peltier element heat absorbing surface 2 a of the Peltier element 2 through the heat conducting grease 4. The heat generated in the Peltier element heat radiating surface 2 b is received at the heat radiating plate 6 through the heat conducting grease 4, moves to the heat sink 15 through the peat pipe 14, and is dissipated in the heat sink 15 by thermal diffusion.

FIG. 2 is a cross-sectional view of the cooling device 1 of the first preferred embodiment of the present invention, and it is a cross-sectional view of the cooling device 1 seen from this side to the depth side in FIG. 1. FIG. 2 does not show the heat pipes 13 and 14.

As shown in FIG. 2, the spacers 3 are plastic and made of a material having lower thermal conductivity than the heat absorbing plate 5 and the heat radiating plate 6, and they have high stiffness and are not deformed in the cooling device 1 of this preferred embodiment. In attachment, first, the spacers 3 are fixed with screws 8 to the on-the-heat-absorbing-plate spacer attaching surfaces 5 a of the heat absorbing plate 5, and then the heat radiating plate 6 is fixed to the spacers 3 with screws 7. The position of the on-the-heat-absorbing-plate spacer attaching surfaces 5 a where the spacers 3 are attached to the heat absorbing plate 5, and the position of the on-the-heat-absorbing-plate Peltier attaching surface 5 b (a first Peltier element attaching surface) where the Peltier element 2 is attached with the heat conducting grease 4 therebetween, are different (there are steps), where the on-the-heat-absorbing-plate Peltier attaching surface 5 b is positioned closer to the heat radiating plate 6 than the on-the-heat-absorbing-plate spacer attaching surfaces 5 a are. The on-the-heat-absorbing-plate Peltier attaching surface 5 b is located facing the Peltier element heat absorbing surface 2 a of the Peltier element 2. The position where the spacers 3 are attached to the heat radiating plate 6, and the position where the Peltier element 2 is attached with the heat conducting grease 4 therebetween (a second Peltier element attaching surface), are on the same plane 6 a. Because the spacers 3 have low thermal conductivity, it is possible to prevent the reduction of cooling efficiency caused by the conduction of heat from the heat radiating plate 6 to the heat absorbing plate 5 through the spacers 3. In this preferred embodiment, the position where the spacers 3 are attached to the heat radiating plate 6 and the position where the Peltier element 2 is attached with the heat conducting grease 4 therebetween are on the same plane 6 a, but they may be different positions (that is, steps may be formed like the on-the-heat-absorbing-plate spacer attaching surfaces 5 a and the on-the-heat-absorbing-plate Peltier attaching surface 5 b of the heat absorbing plate 5). Also, the on-the-heat-absorbing-plate spacer attaching surfaces 5 a and the on-the-heat-absorbing-plate Peltier attaching surface 5 b may be on the same plane.

Alternatively, without using the screws 8, the length of the screws 7 may be lengthened such that they pass through the spacers 3 to reach the heat absorbing plate 5, so that the spacers 3 and the heat radiating plate 6 can be attached to the heat absorbing plate 5 with the screws 7. However, in this case, the cooling efficiency is reduced when the heat in the heat radiating plate 6 is conducted to the heat absorbing plate 5 through the screws 7. Accordingly, attaching the heat absorbing plate 5 and the heat radiating plate 6 with the screws 7 and the screws 8 provides heat insulation and enhanced cooling efficiency.

The thickness of the spacers 3 (i.e. the interval between the on-the-heat-absorbing-plate spacer attaching surfaces 5 a and the heat radiating plate 6) is equal to the total of the thickness of the Peltier element 2, a necessary minimum thickness of the heat conducting grease 4, and the difference (step height) between the on-the-heat-absorbing-plate Peltier attaching surface 5 b and the on-the-heat-absorbing-plate spacer attaching surfaces 5 a. When the position where the spacers 3 are attached to the heat radiating plate 6 and the position where the Peltier element 2 is attached with the heat conducting grease 4 therebetween are different, the thickness of the spacers 3 is equal to the above-mentioned total thickness plus the difference between the position where the spacers 3 are attached to the heat radiating plate 6 and the position where the Peltier element 2 is attached with the heat conducting grease 4 therebetween. That is to say, the spacers 3 are located between the heat absorbing plate 5 and the heat radiating plate 6 in parallel with the Peltier element 2, and they are provided to define the opposing distance between the on-the-heat-absorbing-plate Peltier attaching surface 5 b of the heat absorbing plate 5 (the first Peltier element attaching surface) and the surface of the heat radiating plate 6 (the second Peltier element attaching surface) that is located opposite the on-the-heat-absorbing-plate Peltier attaching surface 5 b.

The necessary minimum thickness of the heat conducting grease 4 in this preferred embodiment is a thickness that satisfies the following two conditions. A first condition is, a thickness of the heat conducting grease 4 determined when the pressure applied to the Peltier element 2 is a given pressure not more than the permissible pressure, when the heat conducting grease 4 is applied on both surfaces of the Peltier element 2 and both surfaces of the Peltier element 2 are sandwiched and pressurized between plates larger than the Peltier element 2. At this time, due to the applied surface pressure, extra heat conducting grease 4 squeezes out to the sides of the Peltier element 2 (the sides where no heat conducting grease 4 is applied). A second condition is such a thickness of the heat conducting grease 4 that no gaps form between the Peltier element 2 and the heat absorbing plate 5 and between the Peltier element 2 and the heat radiating plate 6, which is determined according to the degrees of flatness and the surface roughness of the surfaces of the Peltier element 2, the heat absorbing plate 5, and the heat radiating plate 6.

By using the spacers 3 whose thickness is determined as described above (i.e. the spacers 3 are defined to a sum of the thickness of the Peltier element 2 and the thickness of the heat conducting grease 4 determined when a given pressure not more than the permissible pressure of the Peltier element 2 is applied), the pressure applied to the Peltier element 2 provided between the heat absorbing plate 5 and the heat radiating plate 6 with the heat conducting grease 4 therebetween is a given pressure not more than the permissible pressure, and the attachment is easy. Also, the heat conducting grease 4 ensures intimate contact at the contact surface between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5 and the contact surface between the Peltier element heat radiating surface 2 b and the heat radiating plate 6.

FIG. 3 is a cross-sectional view of the cooling device 1 according to the first preferred embodiment of the present invention, and it is a cross-sectional view of the cooling device 1 seen from the left side to the right side in FIG. 1. FIG. 3 does not show the heat radiating plate 6 and the heat pipe 14.

As shown in FIG. 3, on the heat absorbing plate 5, Peltier elements 2 with the heat conducting grease 4 (not shown) and spacers 3 are provided. A plurality of Peltier elements 2 are separated from each other. The Peltier element control signal lines 9 connected to the Peltier elements 2 are drawn out from the intervals between the separated spacers 3.

The volume of the Peltier element 2 varies as the temperature varies while operating. The volume of the Peltier element heat absorbing surface 2 a shrinks as the temperature falls, and the volume of the Peltier element heat radiating surface 2 b expands as the temperature rises. Then, when the interval between adjacent Peltier elements 2 is insufficient, the Peltier element heat radiating surface 2 b expands to come in contact with the adjacent Peltier element 2, and the expansion is hindered. This causes breakage and performance degradation of the Peltier elements 2. Accordingly, the Peltier elements 2 are separated at sufficient intervals such that they are not influenced by the volume expansion. Also, since a gap exists between adjacent Peltier elements 2, it is possible to ensure space for accumulating extra heat conducting grease 4 squeezing out from between the Peltier elements 2 and the heat absorbing plate 5 and between the Peltier elements 2 and the heat radiating plate 6. That is to say, a plurality of Peltier elements 2 are arranged on one heat absorbing plate 5 at given intervals that permit extensions of the Peltier elements 2 or the spacers 3. Thus, it is possible to prevent extra heat conducting grease 4 from remaining between the Peltier elements 2 and the heat absorbing plate 5 and between the Peltier elements 2 and the heat radiating plate 6, and it is possible to prevent application of excessive pressure to the Peltier elements 2 and to prevent reduction of thermal conduction efficiency.

Thus, intimate contact is ensured at the contact surface between the heat absorbing surfaces of the Peltier elements and the heat absorbing plate 5 (an object to be cooled) and the contact surface between the heat radiating surfaces of the Peltier elements and the heat radiating plate 6 (a cooling part), and also the attachment is easy.

Second Preferred Embodiment

In the first preferred embodiment, the heat conducting grease 4 is used as a heat conducting member between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5 and between the Peltier heat radiating surface 2 b and the heat radiating plate 6. In a second preferred embodiment of the present invention, a heat conducting rubber sheet 16 is provided as a heat conducting member between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5. In other respects, the structure and operation are the same as those of the first preferred embodiment and they are not described here again.

FIG. 4 is a cross-sectional view of a cooling device 1 according to the second preferred embodiment of the present invention, and it is a cross-sectional view of a cooling device 1 seen from this side to the depth side in FIG. 1. FIG. 4 does not show the heat pipes 13 and 14.

As shown in FIG. 4, a heat conducting rubber sheet 16 is provided as a heat conducting member between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5. The heat conducting rubber sheet 16 is a highly heat conducting rubber sheet having elasticity, and it is a heat conducting member used to enhance the heat conductivity by filling gaps formed due to the degree of flatness and the surface roughness at the contact surface between the Peltier element 2 and the heat absorbing plate 5.

The heat conducting rubber sheet 16 is compressed and deformed when subjected to surface pressure. The thickness of the spacers 3 (i.e. the interval between the on-the-heat-absorbing-plate spacer attaching surfaces 5 a and the heat radiating plate 6) is equal to the total of the thickness of the Peltier element 2, a necessary minimum thickness of the heat conducting grease 4 between the Peltier element 2 and the heat radiating plate 6, a thickness under necessary pressure of the heat conducting rubber sheet 16 between the Peltier element 2 and the heat absorbing plate 5, and the difference (step height) between the on-the-heat-absorbing-plate Peltier attaching surface 5 b and the on-the-heat-absorbing-plate spacer attaching surfaces 5 a. The necessary minimum thickness of the heat conducting grease 4 is as described in the first preferred embodiment. The thickness under necessary pressure of the heat conducting rubber sheet 16 is a thickness determined when a given pressure not more than the permissible pressure of the Peltier element 2 is applied to the heat conducting rubber sheet 16. The heat conducting rubber sheet 16 may be provided both between the Peltier element 2 and the heat absorbing plate 5 and between the Peltier element 2 and the heat radiating plate 6, or may be provided only between the Peltier element 2 and the heat radiating plate 6. That is to say, the heat conducting rubber sheet 16 may be provided in at least one of the gaps between the Peltier element 2 and the heat absorbing plate 5 and between the Peltier element 2 and the heat radiating plate 6.

Thus, the pressure applied to the Peltier element 2 can be adjusted by designing the dimensions of the spacers 3 according to the amount of compressive deformation of the heat conducting rubber sheet 16, and the attachment is facilitated. The heat conducting rubber sheet 16 is compressed between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5, and so it is deformed to come in intimate contact with the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5. Also, the reactive force of the deformed heat conducting rubber sheet 16 applies a certain pressure, not more than the permissible pressure, to the Peltier element, and ensures intimate contact at the contact surface between the Peltier element heat absorbing surface 2 a and the heat absorbing plate 5 and the contact surface between the Peltier element heat radiating surface 2 b and the heat radiating plate 6.

Third Preferred Embodiment

In the first and second preferred embodiments, the heat radiating plate 6 is fixed to the spacers 3 with the screws 7. In a third preferred embodiment of the present invention, the heat radiating plate 6 is fixed by plate springs 17 attached to the spacers 3 with screws 18. In other respects, the structure and operation are the same as those described in the first and second preferred embodiments and they are not described again here.

FIG. 5 is a cross-sectional view of a cooling device 1 according to the third preferred embodiment of the present invention. As shown in FIG. 5, the plate springs 17 deform as they apply pressing force to the heat radiating plate 6, and pressurize the Peltier element 2 by applying reactive force to the heat radiating plate 6 according to the amount of deformation. That is to say, the plate springs 17 presses the heat radiating plate 6 toward the heat absorbing plate 5. The pressure applied to the Peltier element 2 can be kept at a given pressure by designing the plate springs 17 such that the pressure applied to the Peltier element 2 is a given pressure not more than the permissible pressure of the Peltier element 2.

Thus, by providing the plate springs 17, in addition to the effects of the second preferred embodiment, the pressure applied to the Peltier element 2 can be more accurately kept constant, and the attachment is facilitated.

Alternatively, without using the screws 8, the length of the screws 18 may be lengthened such that they pass through the spacers 3 to reach the heat absorbing plate 5, so that the spacers 3 and the plate springs 17 are attached to the heat absorbing plate 5 with the screws 18. However, in this case, the cooling efficiency is reduced when the heat of the heat radiating plate 6 is conducted to the heat absorbing plate 5 through the screws 18, and attaching the heat absorbing plate 5 and the heat radiating plate 6 with the screws 18 and the screws 8 provides thermal insulation and enhanced cooling efficiency.

While, in the third preferred embodiment, a heat conducting rubber sheet 16 is provided between the Peltier element 2 and the heat absorbing plate 5, heat conducting grease 4 may be provided in place of the heat conducting rubber sheet 16. In this case, the effects of the third preferred embodiment are obtained in addition to the effects of the first preferred embodiment.

While the invention has been described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is understood that numerous other modifications and variations can be devised without departing from the scope of the invention. 

1. A cooling device comprising: a Peltier element having a heat absorbing surface and a heat radiating surface that are opposite each other; a heat absorbing plate having a first Peltier element attaching surface and located with said first Peltier element attaching surface facing said heat absorbing surface of said Peltier element; a heat radiating plate having a second Peltier element attaching surface and located with said second Peltier element attaching surface facing said heat radiating surface of said Peltier element; heat conducting members having viscosity or elasticity and provided between said heat absorbing surface and said first Peltier element attaching surface and between said heat radiating surface and said second Peltier element attaching surface; and a spacer provided between said heat absorbing plate and said heat radiating plate in parallel with said Peltier element and defining an opposing distance between said first and second Peltier element attaching surfaces.
 2. The cooling device according to claim 1, wherein said spacer defines said opposing distance to a sum of a thickness of said Peltier element and a thickness of said heat conducting member determined when a given pressure not more than a permissible pressure of said Peltier element is applied.
 3. The cooling device according to claim 1, wherein said heat conducting members are heat conducting grease.
 4. The cooling device according to claim 3, wherein a heat conducting rubber sheet is used in place of said heat conducting grease in at least one of gaps between said heat absorbing surface and said first Peltier element attaching surface and between said heat radiating surface and said second Peltier element attaching surface.
 5. The cooling device according to claim 1, wherein said spacer is made of a material having lower thermal conductivity than said heat absorbing plate and said heat radiating plate.
 6. The cooling device according to claim 1, wherein said heat absorbing plate and said heat radiating plate are fixed to said spacer with different screws.
 7. The cooling device according to claim 1, wherein said Peltier element includes a plurality of Peltier elements, and said plurality of Peltier elements are arranged on one said heat absorbing plate at given intervals that permit extensions of said Peltier elements or said heat conducting member.
 8. The cooling device according to claim 1, further comprising a spring that presses said heat radiating plate toward said heat absorbing plate. 